A project to save Britain’s largest species of spider from being dying out has
been hailed a success after spiders released into the wild have bred
successfully for the first time.

For arachnophobes it may not be welcome news – Britain’s largest spider is starting to make a comeback.

The fen raft spider, which can have an adult leg span of up to four inches across and bodies an inch long, has successfully bred at a new location in the wild for the first time in more than 20 years following a reintroduction programme to save them from dying out.

The spiders, which earn their name due to their ability to sit on top of the water surface, are one of the country’s rarest arachnids and had become restricted to just three tiny sites in the fens of Norfolk, Sussex and south Wales.

Now conservation experts believe the dark brown creatures have established themselves in a new area after discovering spiders they released into the wild two years ago are breeding by themselves.

They have found more than 40 nursery webs each containing up to 700 spiderlings at the Castle Marshes nature reserve, near Beccles, Suffolk.

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Dr Helen Smith, an ecologist who has been leading the reintroduction programme, said it marked a major “milestone” in the attempt to help the spiders recover.

She said: “Finding that they were out there and breeding successfully was very exciting. I am cautiously optimistic about their future at these new sites.

“When undertaking translocation projects like this you can never be sure how successful it will be, so this makes all the hard work feel worthwhile. The fen raft spider is beautiful and charismatic, but it also tells us the condition of the habitat that has been restored.”

The breeding spiders were found after nearly 1,600 hand-reared spiderlings were released at Castle Marshes in 2010 as part of a desperate attempt to help the population of the fen raft spider recover.

Dr Smith reared thousands of the baby spiders in individual test tubes in her kitchen as part of the project after collecting mothers from Redgrave and Lopham Fen Nature Reserve.

The spiders were reared individually to avoid them from attacking each other and fed fruit flies almost around the clock to keep them alive. In total around 7,000 spiderlings have been released with the help of volunteers and schemes at 10 zoos around the country.

A three months old the spiderlings were released at a number of sites in Suffolk and East Anglia where fen raft spiders were thought to be widespread once.

Despite their large size, the species were only discovered in the UK in 1956, by which time large areas of their potential habitat had already been destroyed through draining of the fens and agriculture. They have experienced similar declines in other parts of Europe.

The spiders hunt by perching with their back legs on a stem and their front legs resting on the surface of the water to detect vibrations.

They can rush across the water, using surface tension to support their weight, to seize their prey, which include insects that have fallen into the water and even small fish.

David Heaver, senior invertebrate specialist from Natural England who have been funding the reintroduction project along with Suffolk Wildlife Trust, said they now hoped the spiders might start to spread to new areas by themselves.

He said: “Hand rearing the spiderlings is very intensive and takes a lot of time as they all need to be individually fed at the right time and their bedding needs to be changed individually as well.

“Previously East Anglia was awash with marshes so there is no reason to think that the spiders were not widespread. They are very sensitive and can be lost quite easily. But it seems that if you get things right you can get them back too.

“If we can get them into the marsh drainage systems then they could spread around quite a long way on their own – their ability to raft downstream is quite large.”